Riding After Blood Donation? Weakness? Low Blood Pressure?

Couple of years ago I rode to UBS to donate and when it was over, chugged a solf drink and climbed back on the bike without waiting longer to recover. On the way home, about 4-5 miles, I aired out the bike, pedaling at 120+ rpm for 2-3 miles. Couple of miles to go, I started feeling like I was gonna faint off the bike, so I stopped at a bench on Glenna Goodacre, leaned over, and ate an orange from my back pack. When I got home, I lay down on the floor for a while and then took my blood pressure. It showed 80/55.

Today, I drove to donate blood, then rode in the p.m. Felt light headed most of the way, though I was a long way from fainting. Cut my ride short. BP showed 106/65.

Anybody else ridden soon after blood donation?

Year later and no fainting on the bike. So I guess the problem is not too progressive.

I did have the problem other times though, back in 2008 and 2009. Probably five times total.

Once I had the bright idea of doing intervals up and down the canyon sides on East Broadway. Uphill, downhill, build up speed, uphill, downhill. A little of that and I was pooped. Rode toward home and got through the Broadway Railroad underpass when I couldn't continue. Lay down on the grass alongside the Medlock's building until able to ride home.

Another time on Canyon Drive, not riding hard but felt faint, so I lay on the grass at streamside, head on backpack, for 15 minutes.

Another time it was hot and I'd eaten a meal a bit earlier, I had to crash out under a skinny tree at what used to be Lubbock's public pool in Mackenzie Park.

More recently, think it was in 2010, I had to lie down at Broadway & Canyon Lakes Drive, right on the frisbee course. And again under the big elms at lakeside near the park entrance.

I'd bet that each time my bp was low. But don't see any uniform cause. Sometimes heat, sometimes hard riding, sometimes too soon after too big a meal. Sometimes after a sugary drink (possible hypoglycemia). Sometimes none of the above.

Lowish blood pressure seems to be common among cyclists. A frequent symptom is feeling faint when standing suddenly after lying down. Unlike high bp, low bp is not considered a disease.

Fainting when riding the bike is not good at all, because of the possibility of an accident, if for no other reason. I'd say that if a rider feels faint, he needs to stop and get off. Puking is one thing, just watch where you hurl; fainting is something else.

While very low bp might definitely be a health problem -- 00/00 and you are dead -- numbers a bit lower than the "normal" 120/80 are considered desirable not harmful. Don't know about 80/55, especially when one is exercising. That upper number is getting down there.